Nickel alloy



1957 P. E. HEGMEGEE, JR 2,730,544

NICKEL ALLOY Filed Oct. 12, 1954 INVENTOR P901 A him/1:055 Zn ATTORNEY U ite SW Pat NICKEL ALLOY Paul Edward Hegmegee, Jr., Clifton, N. J., assignor to The International Nickel Company, Inc., New York, N. Y., acorporation' of Delaware Application October 12, 1954, Serial No. 461,875

4 Claims. (Cl. 75-470) alloys are useful in many applications where corrosion resistance and a high combination of mechanical properties are required. Heretofore, some difiicul'ties have been experienced in providing nickel alloy castings having satisfactory machinability for industrial purposes. In order to provide nickel alloy castings having satisfactory machinability, the resort has been had to sulfur-containing alloys. Such castings had satisfactory machinability but were susceptible to cracking, particularly when produced in the form of investment castings and this cracking led to an undesirably high number of rejections. It had been found that nickel copper-sili'con castings were free of cracking and had acceptable ma'chinability in the annealed condition. However, it was found that even these nickel-copper-silicon castings occasionallypresented erably in a manner which could not be explained on the basis of hardness. In other words, hardness was not a reliable index to indicate the machinability of these castings.

It, has now been discovered that through special processing in the molten stage, nickel-copper-silicon alloy castings can be provided which have greatly improved machinabi'lity and which have a high combination of physical properties.

It is an object of the present invention to provide a method for producing nickel-copper-silicon alloy castings having improved machinability.

Another object of the invention is to provide a machinable nickel-copper-silicon alloy casting which has a high combination of physical properties.

It is a further object of the invention to provide machinable graphitic nickel-copper-silicon alloys having a distinctive microstructure and having a high combination of mechanical properties.

Other objects and advantages of the invention will become apparent from the following description taken in conjunction with the drawings in which:

Figure l is a reproduction of a photomicrograph taken at 250 diameters and depicting the microstructure of a cast alloy produced in accordance with the present invention; and

Figure 2 is a reproduction of a photomicrograph taken at 1000 diameters and depicting the characteristic featheredged structure of a graphite nodule in a casting produced as contemplated by the present invention.

Broadly stated, the present invention comprises a special graphitic nickel-copper-silicon alloy and the process for producing the same. The process according to the invention comprises establishing a bath of molten nickel alloy containing about 0.5% to 3.5% silicon, about 0.4%

-' in the intended service.

to about 0.7% carbon, up to about 35% copper, up to about 2.5 manganese, and up to about 5 iron; conditioning. the bath with an addition of about 1% to about 2% calcium carbide; introducing. about 0.1% to about 0.2% magnesium into theconditioned bath; and casting metal from: the thus-treated bath to provide castings containing nodular graphite and containing about 0.5 to 3.5% silicon, about 0.4% to 0.7% carbon, up to about 2.5% manganese, up to about 5% iron, about 25% to 35% copper, about 0.2% to 0.2% magnesium, less than about 0.01% calcium, and the balance essentially nickel. Preferably, the calcium carbide addition is made while the bath is superheated about 200 F. above the normal casting temperature for the metal, e. g., a superheated temperature of about 3000 F. After the calcium carbide addition is complete, it is preferred to skim off resulting slagand to cool the bath to the casting temperature range of about 2500 to 2800 F. before adding the required magnesium.

Castings produced in accordance with the invention contain the foregoing amounts of magnesium in order to insure the presence of nodular graphite in the castings. Calcium can be detected spectrographically in the castings but the calcium content is of a low order less than about 0.01%. The combined use of magnesium and calcium as calcium: carbide as described herein is essential to obtain, in combination with the remainder of the composi ion, the feather-edged graphite nodules required in accordance with the present invention. It is preferred that the copper content of the alloy be maintained in the range of 25% to 32% and that the magnesium content be maintained in the range of about 0.08% to about 0.15%. It is important that the silicon content of the casting be not less than about 0.5% as otherwise the gall resistance, the wear resistance and the mechanical properties of the re sult'i'n'g castings are reduced and the castings tend to become magnetic. On the other hand, the silicon content should not exceed about 3.5% as otherwise it is difiicult to obtain necessary ductility in the resulting castings and it becomes difiicult to produce nodular graphite. More preferably, silicon is maintained in the range of about 2% to 3% to provide the best combination or" mechanical properties with gall and wear resistance. The copper content, in combination with the contents ofother ingredients of the'castings, likewise contributes importantly to the properties of the castings, including hardenability and high strength, as compared to similar alloys free of copper or low in copper. The copper content should not be less than about 25% in order to enable production of desired strength and hardenability but should not exceed about 35% as otherwise the rnachinability and ductility of the castings is impaired. The carbon content of castings contemplated in accordance with the invention should be maintained between about 0.4% and about 0.7% preferably about 0.5% to about 0.7%, in order to provide adequate machinab'ility and strength in the re sulting castings. The nickel content of castings produced in accordance with the invention will usually be between about 62% and about 68%. Besides the elements in the amounts specified herein'before, castings comprehended within the invention may contain relatively minor amounts of elements such as iron, manganese, etc, which do not detr'imentally affect the basic and novel properties of castings produced according to the invention. Thus, iron may be present in amounts upto about 5%, e. g, about 0.5% to 5%, without detrimentally affecting the properties of the castings. if non-magnetic castings are required, the iron content of the castings usually should not exceed about 2%, depending upon the content of other elements, such as silicon, which reduce the mag netic susceptibility and the required Curie temperature In the castings produced in accordance with the invention, manganese is a desirable constituent which promotes fluidity and a sound casting. Accordingly, manganese is desirably present in amounts up to about 2.5%. The sulfur content of alloys produced in accordance with the present invention is low i. e., below about 0.02%, e. g., about 0.002% to 0.016%. Preferably, castings produced according to the invention are devoid of elements such as titanium and zirconium, as these elements deleteriously aifect the graphite formed in the castings.

The castings contemplated in accordance with the present invention may also contain up to about 2% of cobalt and up to about 1% of chromium without affecting the basic and novel characteristics thereof. Impurities such as phosphorus, zinc, lead, etc., preferably should be avoided and usually should not be present in amounts exceeding a total of about 0.1%. All percentages referred to herein are by weight.

It has been found that castings having the compositions and produced in the manner described hereinbefore are characterized by the presence of graphite in a distinctive nodular form. This distinctive microstructural characteristic is illustrated in the accompanying Figures 1 and 2 which depict the feather-edged graphite nodules produced in castings contemplated in accordance with the present invention. It has been found that castings exhibiting this distinctive microstructural characteristic exhibit an improved combination of mechanical and physical properties as compared to similar non-graphitic alloys and even to similar graphitic alloys which do not exhibit the aforementioned distinctive microstructure. In general, the machinable castings produced in accordance with the present invention will exhibit mechanical properties within the following ranges of values:

As-east Annealed In order to give those skilled in the art a better understanding of the invention, the following example is given:

A melt of nickel alloy containing about 29.3% copper, about 2.6% silicon, about 0.7% manganese, and about 1.4% iron was established and the carbon content thereof was adjusted to about 0.6%. An addition of about 1.5% by weight of powdered calcium carbide was made to the surface of said melt held in the furnace and the carbide was stirred into the melt until the addition reactions, as evidenced by burning, etc., had ceased. About 0.15% of magnesium as a nickel-magnesium alloy was then added and stirred into the melt and metal from the thustreated melt was cast into castings, including tensile test bars and test plates measuring 6 x 3" x A Upon analysis, these graphitic castings were found to contain about 0.004% sulfur, about 0.15% magnesium, and less than about 0.01% calcium. Similar castings were produced from the non-graphitic basic nickel-copper alloy. Tensile specimens of graphitic castings produced in the foregoing manner and in accordance with the invention displayed the following properties:

As Cast Annealed 1 Yield strength, p. s. i. (0.5% 65, 500 34, 000 Hardness (Rockwell B) 88 80 Elongation, Percent 21 32 1 Heat to 1,600 F., hold one hour, furnace cool to 1,300 F., oil quench.

45,500 p. s. i., a Rockwell B hardness of 85, and an elongation of 38% and in the annealed condition had a tensile strength of 72,400 p. s. i., a yield strength of 35,400 p. s. i., a Rockwell B hardness of 66, and an elongation of 37.5%.

The greatly improved machinability of the graphitic castings made in accordance with the invention as compared to the otherwise similar non-graphitic castings is strikingly demonstrated by drilling tests made upon the test plate castings described hereinbefore. In making the drilling tests, unlubricated -inch diameter drills running at 5100 revolutions per minute and at a feed of feet per minute were employed. The drills had an included point angle of about In each case, a freshlyground drill was employed and holes were drilled in the test plates until the drill would not complete a hole or until drilling pressure became excessive. Under these conditions, the following results were obtained:

were finely broken, whereas the chips produced in drilling the non-graphitic base composition tended to curl. The graphitic alloy contemplated by the invention responded to the drilling test in a manner similar to that of other nickel alloys known to be free-machining.

A further improvement which characterizes the graphitic castings produced in accordance with the invention is the unexpectedly improved resistance to galling and wear. It has been known heretofore that non-graphitic nickel-copper-silicon base alloys had acceptable resistance to galling and wear. However, prior attempts to include graphite in such alloys had always resulted in drastic reduction of gall and wear resistance. Tests to evaluate the resistance of the graphitic nickel-copper-silicon castings contemplated by the present invention to the effects of galling and wear have shown that the graphite present in these alloys does not injure these properties of the castings. On the contrary, the tests have shown that the castings resist seizing and have satisfactory wearing properties, particularly in cases where lubrication can be supplied.

It will be appreciated that, in the absence of the special treatments with calcium carbide and magnesium contemplated in accordance with the present invention, the carbon-containing nickel-copper alloy castings have graphite present in flake form and have reduced physical properties. It appears that the additions of calcium carbide and magnes ium act synergistically to improve the properties of the special nickel-copper alloy castings and to impart thereto the characteristic graphite structure described hereinbefore. Thus, separate portions of the same car hon-containing melt described hereinbefore were treated with individual additions of 1.5% calcium carbide and of 0.15 magnesium and the properties of the resulting castings were as follows in the as-cast condition and after the same annealing treatment as described hereinbefore:

In view of the foregoing data, it will be seen that the properties of the casting produced by means of a combined addition of calcium carbide and magnesium as described hereinbefore are much higher than the properties of castings produced using single additions of calcium carbide or magnesium. Furthermore, it is important that the calcium carbide addition precede the magnesium addition in order to obtain the special new results contemplated in accordance with the invention. It has also been established that calcium metal and similar calcium compounds, e. g., calcium silicide, nickel calcium, etc., are not equivalents to calcium carbide for purposes of the present invention. When such other forms of calcium are employed, the characteristic feather-edged graphite nodules are not obtained and the improved combination of properties which characterize castings produced in accordance with the present invention are not achieved.

As noted hereinbefore, annealed castings produced in accordance with the invention are softer and are characterized by improved machinability as compared to castings in the as-cast condition. Annealing should be conducted at a temperature of at least about 1600 F., e. g., about 1600 to 1700 F., and should be followed by relatively rapid cooling, e. g., an oil quench. In treating castings of intricate design, it is preferred that the castings be slowly cooled from the annealing temperature to an intermediate temperature, e. g., 1300 F., before quenching so as to avoid cracking. Castings produced according to the invention may be age hardened to hardnesses exceeding that found in the as-cast condition by heating at temperatures on the order of about 1000 to 1200 F. For example, a treatment at a temperature of about 1100 F. for about 4 to 6 hours is preferred. Castings which have been annealed or annealed and age hardened have a more homogeneous structure than that found in the ascast condition. 7

The cast alloys produced in accordance with the present invention may be cast into investment molds to pro vide products having an acceptable surface finish. The metal processed in accordance with the present invention may also be produced in the form of sand castings. Products produced in accordance with the present invention include caps, frames, gimbals, etc., which are used in a gyroscope for an automatic pilot, fishing reel parts, pumps and pump impellers, filter plates, valve bodies, bushings, fittings, and various other castings.

Although the present invention has been described in conjunction with preferred embodiments, it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the invention, as those skilled in the art will readily understand. Such modifications and variations are considered to be within the purview and scope of the invention and appended claims.

I claim:

1. The method for producing improved graphitic nickel-copper-silicon castings which comprises establishing a bath of a nickel alloy containing about 0.5% to 3.5% silicon, about 0.4% to 0.7% carbon, about 25% to about 35% copper, up to about 5% iron and up to about 2.5% manganese, reacting said bath with about 1% to 2% of calcium carbide, adding about 0.1% to about 0.2% magnesium to the thus-treated bath, and thereafter casting metal from the bath to provide graphitic castings containing about 0.5% to 3.5% silicon, about 0.4% to 0.7% carbon, about 25% to 35% copper, up to about 5% iron, up to about 2.5% manganese, about 0.02% to 0.2% magnesium, calcium up to about 0.01%, and the balance essentially nickel, said castings containing nodular graphite and being characterized by a high combination of mechanical properties and by improved machinability.

2. The method for producing improved gnaphitic nickel-copper-silicon castings which comprises establishing a bath of a nickel alloy containing about 2% to 3% silicon, about 0.5% to 0.7% carbon, about 25 to 32% copper, up to about 5% iron and up to about 2.5% manganese, reacting said bath with about 1% to 2% calcium carbide, adding about 0.1% to 0.2% magnesium to the thus-treated bath and thereafter casting metal from the bath to provide graphitic castings containing about 2% to 3% silicon, about 0.5% to 0.7% carbon, about 25% to 32% copper, up to about 5% iron, up to about 2.5 manganese, about 0.02% to 0.2% magnesium, calcium up to about 0.01%, and the balance essentially nickel, said castings containing nodular graphite and being characterized by a high combination of mechanical properties and by improved machinability.

3. As a new article of manufacture, an improved machinable nickel-copper-silicon alloy casting containing nodular graphite and having a high combination of strength and ductility, and containing about 0.5 to 3.5% silicon, about 25% to 35% copper, about 0.4% to 0.7% carbon, up to about 2.5% manganese, up to about 5% iron, about 0.02% to 0.2% magnesium, calcium up to about 0.01%, and the balance essentially nickel.

4. As a new article of manufacture, an improved machinable nickel-copper-silicon alloy casting containing nodular graphite and having a high combination of strength and ductility, and containing about 2% to 3% silicon, about 25 to 32% copper, about 0.5% to 0.7% carbon, up to about 2.5% manganese, up to about 5% iron, about 0.08% to 0.15% magnesium, calcium up to about 0.01%, and the balance essentially nickel.

References Cited in the file of this patent UNITED STATES PATENTS 2,253,382

Lee Aug. 19, 1941 2,355,059 Eash Aug. 8, 1944 2,485,760 Millis et al. Oct. 25, 1949 2,568,013 Lee et al Sept. 18, 1951 FOREIGN PATENTS 700,626

OTHER REFERENCES Great Britain Dec. 9, 1953 

1. THE METHOD FOR PRODUCING IMPROVED GRAPHITIC NICKEL-COPPER-SILICON CASTINGS WHICH COMPRISES ESTABLISHING A BATH OF A NICKEL ALLOY CONTAINING ABOUT 0.5% TO 3.5% SILICON, ABOUT 0.4% TO 0.7% CARBON, ABOUT 25% TO ABOUT 35% COPPER, UP TO ABOUT 5% IRON AND UP TO ABOUT 2.5% MANGANESE, REACTING SAID BATH WITH ABOUT 1% TO 2% OF CALCIUM CARBIDE, ADDING ABOUT 0.1% TO ABOUT 0.2% MANGNESIUM TO THE THUS-TREATED BATH, AND THEREAFTER CASTING METAL FROM THE BATH TO PROVIDE GRAPHITIC CASTINGS CONTAINING ABOUT 0.5% TO 3.5% SILICON, ABOUT 0.4% TO 0.7% CARBON, ABOUT 25% TO 35% COPPER, UP TO ABOUT 5% IRON, UP TO ABOUT 2.5% MANGANESE, ABOUT 0.02% TO 0.2% MAGNESIUM, CALCIUM UP TO ABOUT 0.01%, AND THE BALANCE ESSENTIALLY NICKEL, SAID CASTINGS CONTAINING NODULAR GRAPHITE AND BEING CHARACTERIZED BY A HIGH COMBINATION OF MECHANICAL PROPERTIES AND BY IMPROVED MACHINABILITY. 